The present invention relates to discharge ports in a pressurized vessel used to process biomass feed materials. In particular, the present invention relates to an assembly of valves and nozzles in a discharge port of a pressurized vessel.
Biomass feed material is typically processed in a vertical pressurized vessel. The feed material enters an upper inlet of the vessel, is cooked or otherwise processed in the vessel and is discharged from a port at the bottom of the vessel. The biomass feed material may be pre-treated in the vessel, such as by steaming or by hydrolysis, or the vessel may digest the biomass feed material to convert the biomass to fibers or otherwise process the biomass. In addition, the pressurized vessel may be a steaming and pressurizing device wherein the nozzle in the discharge port causes the biomass feed material to undergo steam explosion pulping.
Biomass feed material general includes one or more of cellulosic feed material, e.g., wood chips, shredded agricultural residues like straws or corn-stover, fuel energy crops like switchgrass, biomass sorghum or miscanthus, paper pulp and comminuted biomass materials. In addition, the feed material as it flows through the discharge port of the pressurized vessel may be in a slurry including cooking chemicals (which tend to be corrosive) and a large quantity of steam.
Steam explosion pulping typically involves steam used to break apart the cellulosic fiber structure (explosion pulping) of cellulosic biomass feed material. Steam explosion pulping has been used, for example, for enzyme hydrolysis. In steam explosion pulping, pulp is produced from cellulosic biomass feed material by pressurizing feed material with steam and subsequently rapidly reducing the pressure of the feed material impregnated with the steam. The rapid pressure reduction causes steam in the cells of the biomass feed material to expand and burst the cells to produce pulp. The pulp is further processed, for example, with enzymes to convert the pulp to sugars.
In steam explosion pulping, the rapid pressure reduction of the biomass feed material may be performed using a blow-valve at an outlet of a pressurized cooking vessel or conduit. Upstream of the blow-valve, the biomass feed material is pressurized to, for example, 6 bar to 25 bar, and infused with steam. Upstream of the blow-valve, the cellulosic biomass feed material may also be impregnated with chemicals, such as acids, added to a cooking reactor in which the pulp is steamed and held under pressure.
A conventional swept orifice discharge assembly includes a single ball valve or segmented ball valve connected to each discharge outlet at the bottom of a pressurized vessel. The biomass feed material flows through the ball valve and the discharge outlet directly to a blow tank. The ball valve or segmented ball valve is adjustable to control the flow of biomass feed material through the discharge outlet. The flow rate of the biomass feed material from the pressurized vessel is regulated by the ball or segmented ball valve in a conventional orifice discharge assembly.
The biomass feed material frequently contains solid material, e.g., dirt, sand and other hard particles, that wear and damage the components of an orifice discharge assembly. The ball or segmented ball valve of a conventional swept orifice discharge assembly is particularly susceptible to wear and damage from the solid material in the biomass feed material. The adjustability of the ball or segmented ball valve, the large pressure differential across the valve and the solid material in the biomass feed material cause excessive wear to the valve and result in frequent replacement of the valve.
To replace conventional ball valves and segmented ball valves requires the pressurized vessel to be shut down and the flow of biomass feed material to be temporarily stopped while the valve is replaced. In addition to the cost of lost biomass production, the cost of material and labor to replace or repair a ball or segmented ball valve is expensive. Discharge assemblies having multiple adjustable valves and nozzles have been used to provide alternative nozzles and valves for use when one nozzle and valve becomes clogged. The discharge assemblies with multiple valves and nozzles have adjustable valves with each nozzle that are prone to the same wear and damage described above. There is a long felt need for a pressurized vessel discharge assembly that is resistant to solid material in biomass feed material, may be repaired without interrupting the production of biomass feed materials, and is inexpensive to repair or replace.